OFFSHORE ANCHORING SYSTEMS AND ASSOCIATED METHODS

BACKGROUND

Offshore vessels, including marine ships and offshore platforms, utilize anchors to secure the offshore vessel to the seabed of a body of water and thereby secure the offshore vessel at a desired location along the body of water. Some offshore anchors comprise embedded anchors which are embedded in the seabed and are thereby secured to the seabed by the resistance of the surrounding soil. For example, caissons and multiline ring anchors (MRAs) are types of embedded anchors.

BRIEF SUMMARY OF THE DISCLOSURE

An embodiment of a system for anchoring an offshore vessel to a seabed positioned beneath a column of water comprises a foundation comprising a longitudinal axis, a first end, and a second end opposite the first end along the longitudinal axis of the foundation, a keying-flap assembly comprising a plurality of flaps coupled to the foundation whereby the plurality of flaps are configured to pivot relative to the foundation about a plurality of rotational axes associated with the plurality of flaps, the keying-flap assembly having a run-in configuration in which each of the plurality of flaps occupies a first position, and a set configuration in which the plurality of flaps are pivoted from their first positions in alternating rotational directions about their respective rotational axes to occupy a plurality of second positions angularly spaced from their first positions, and a follower extending between a first end and a second end opposite the first end of the follower, the follower configured to apply an extraction force to the foundation to transition the keying-flap assembly from the run-in configuration to the set configuration. In some embodiments, the first positions of the plurality of flaps correspond to vertical positions of the plurality of flaps and the second positions of the plurality of flaps correspond to inclined positions of the plurality of flaps. In some embodiments, the plurality of flaps of the keying-flap assembly are grouped into one or more flap pairs each rotating in opposing rotational directions between their first positions and their inclined positions. In certain embodiments, the plurality of flaps of the keying-flap assembly are grouped into one or more flap pairs each having a Y-shaped profile when the plurality of flaps are in their second positions. In certain embodiments, the plurality of flaps of the keying-flap assembly are grouped into one or more flap pairs spaced at an angle that is equal to or less than 180 degrees when the plurality of flaps are in their second positions. In some embodiments, the system further comprises a plurality of support members coupled to the foundation, and the plurality of flaps of the keying-flap assembly are grouped into one or more flap pairs each coupled to a separate support member of the plurality of support members. In some embodiments, the keying-flap assembly comprises one or more collars each defining a pair of opposed stop surfaces, and the plurality of flaps are angularly spaced from the pair of stop surfaces of the one or more collars when the plurality of flaps are in their first positions, and the plurality of flaps contact the pair of stop surfaces of the one or more collars when the plurality of flaps are in their second positions.

An embodiment of a system for anchoring an offshore vessel to a seabed positioned beneath a column of water comprises a foundation comprising a longitudinal axis, a first end, and a second end opposite the first end along the longitudinal axis of the foundation, a keying-flap assembly comprising a plurality of flaps coupled to the foundation whereby the plurality of flaps are configured to pivot relative to the foundation about a plurality of rotational axes associated with the plurality of flaps, the keying-flap assembly having a run-in configuration in which each of the plurality of flaps occupies a first position, and a set configuration in which the plurality of flaps are pivoted from their first positions about their respective rotational axes to occupy a plurality of inclined positions angularly spaced from their first positions, and a follower extending between a first end and a second end opposite the first end of the follower, the follower configured to apply an extraction force to the foundation to transition the keying-flap assembly from the run-in configuration to the set configuration whereby a first flap of the plurality of flaps applies a first torque to the foundation in a first rotational direction and a second flap of the plurality of flaps applies a second torque to the foundation in a second rotational direction that is opposite the first rotational direction. In some embodiments, the first torque cancels out the second torque resulting in a zero net torque applied to the foundation in response to the application of the extraction force to the foundation by the follower. In some embodiments, the first positions of the plurality of flaps correspond to vertical positions of the plurality of flaps and the second positions of the plurality of flaps correspond to inclined positions of the plurality of flaps. In certain embodiments, at least some of the plurality of flaps rotate in opposed rotational directions between their respective first positions and their respective second positions. In certain embodiments, from a perspective located along the longitudinal axis of the foundation, at least some of the plurality of flaps pivot in a clockwise direction between their respective first positions and their respective second positions and at least some of the plurality of flaps pivot in an opposing counterclockwise direction. In some embodiments, the plurality of flaps of the keying-flap assembly are grouped into one or more flap pairs each rotating in opposing rotational directions between their first positions and their inclined positions. In some embodiments, the keying-flap assembly comprises one or more collars each defining a pair of opposed stop surfaces, and the plurality of flaps are angularly spaced from the pair of stop surfaces of the one or more collars when the plurality of flaps are in their first positions, and the plurality of flaps contact the pair of stop surfaces of the one or more collars when the plurality of flaps are in their second positions.

An embodiment of an offshore vessel comprises a deck, and a winch assembly supported on the deck and connected to the system by one or more tension cables extending between the winch assembly and the foundation of the system, the winch assembly comprising one or more winches and a surface controller configured to automatically confirm the transitioning of the keying-flap assembly into the set configuration in response to monitoring a magnitude of the extraction force applied to the foundation by the follower.

An embodiment of a method for anchoring an offshore vessel to a seabed positioned beneath a column of water comprises (a) penetrating an anchoring system comprising a foundation and a follower through the seabed to an installation depth located beneath the seabed, (b) applying an extraction force to the follower whereby the extraction force is transmitted to the foundation, (c) transitioning a keying-flap assembly comprising a plurality of flaps pivotably coupled to the foundation from a run-in configuration in which each of the flaps occupies a first position to a set configuration in which each of the flaps occupies a second position pivoted from their first position in response to transmitting the extraction force to the foundation, and (d) monitoring by a surface controller spaced from the foundation a magnitude of the extraction force as the keying-flap assembly is transitioned from the run-in configuration to the set configuration to automatically confirm that the keying-flap assembly has successfully transitioned to the set configuration. In some embodiments, the surface controller is configured to identify one or more transition points in the magnitude of the extraction force to automatically confirm that the keying-flap assembly has successfully transitioned to the set configuration. In some embodiments, each of the one or more transition points corresponds to a change in a slope of the magnitude of the extraction force over time. In certain embodiments, transitioning the keying-flap assembly from the run-in configuration to the set configuration comprises pivoting the plurality of flaps in alternating rotational directions relative to the foundation to occupy their respective second positions. In certain embodiments, (c) comprises applying by a first flap of the plurality of flaps a first torque to the foundation in a first rotational direction and applying by a second flap of the plurality of flaps a second torque to the foundation in a second rotational direction that is opposite the first rotational direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

For a detailed description of exemplary embodiments of the disclosure, reference will now be made to the accompanying drawings in which:

FIG. 1 is schematic view of an embodiment of a system for anchoring an offshore vessel to a seabed positioned beneath a column of water in accordance with principles disclosed herein;

FIG. 2 is a cross-sectional view of an embodiment of a foundation of the anchoring system of FIG. 1 in accordance with principles disclosed herein;

FIG. 3 is a side view of an embodiment of a keying-flap assembly of the anchoring system of FIG. 1 in accordance with principles disclosed herein;

FIG. 4 is a schematic view of an anchor handling vessel for handling the anchoring system of FIG. 1 in accordance with principles disclosed herein;

FIG. 5 is another schematic view of the anchoring system of FIG. 1;

FIG. 6 is another cross-sectional view of the foundation of FIG. 2;

FIG. 7 is another side view of the keying-flap assembly of FIG. 3;

FIG. 8 is another schematic view of the anchoring system of FIG. 1;

FIG. 9 is another cross-sectional view of the foundation of FIG. 2;

FIG. 10 is another side view of the keying-flap assembly of FIG. 3;

FIG. 11 is another schematic view of the anchoring system of FIG. 1;

FIG. 12 is another cross-sectional view of the foundation of FIG. 2;

FIG. 13 is another side view of the keying-flap assembly of FIG. 3;

FIG. 14 is another schematic view of the anchoring system of FIG. 1;

FIG. 15 is another cross-sectional view of the foundation of FIG. 2;

FIG. 16 is another side view of the keying-flap assembly of FIG. 3;

FIG. 17 is schematic view of another embodiment of a system for anchoring an offshore vessel to a seabed positioned beneath a column of water in accordance with principles disclosed herein;

FIG. 18 is a cross-sectional view of an embodiment of a foundation of the anchoring system of FIG. 17 in accordance with principles disclosed herein;

FIG. 19 is a graph illustrating extraction force as a function of keying distance;

FIG. 20 is a schematic view of an offshore vessel in accordance with principles disclosed herein;

FIG. 21 is a block diagram of an embodiment of a computer system in accordance with principles disclosed herein;

FIG. 22 is a flowchart of an embodiment of a method for anchoring an offshore vessel to a seabed positioned beneath a column of water in accordance with principles disclosed herein;

FIG. 23 is a diagram of a soil failure mechanism around a Y-shaped keying-flap system;

FIG. 24 is a graph illustrating normalized axial capacity of different Y-shaped keying-flap systems as a function of adhesion factor and flap angle;

FIG. 25 is another diagram of a Y-shaped keying flap system of an anchoring system in both run-in and set configurations;

FIG. 26 is a graph illustrating the non-dimensional value N_a as a function of flap angle and flap length of the stiffener; and

FIG. 27 is another graph illustrating normalized axial capacity as a function of adhesion factor and keying flap length for different stiffeners.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to...” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Further, as used herein, the terms “approximately,” “about,” “substantially,” and the like mean within 10% (i.e., plus or minus 10%) of the recited value. Thus, for example, a recited angle of “about 80 degrees” refers to an angle ranging from 72 degrees to 88 degrees.

As described above, caissons and MRAs are types of embedded anchors. MRAs were originally developed for securing floating offshore wind turbines (FOWTs) but are applicable for a variety of offshore applications given their deep embedment into strong soil permits the achievement of high load capacity with an anchor that is comparably smaller and lighter (and thus less expensive) than conventional caissons. However, given that MRAs are generally shorter than conventional caissons, additional features such as support members (sometimes referred to as “stiffeners” and “wing plates”) are relied on to achieve parity in load capacity with caissons having a comparable diameter. Additionally, while support members can be effective in increasing the horizontal load capacity of the MRA, they are generally ineffective at improving vertical load capacity. Further, single keying flaps may improve vertical load capacity to a degree, conventional single keying flaps typically permit an undesirable amount of upward travel of the anchor during installation due to a delay in the keying action of the flap resulting from reversals in motion of the anchor during installation. Further, conventional single keying flaps tend to apply a net rotational torque to the anchor in response to the application of a vertically directed load to the anchor during installation. The net torque applied to the anchor may destabilize the anchor during installation, increasing the likelihood of a failure in properly setting the anchor within the foundation.

Accordingly, embodiments of anchoring systems are described herein having a plurality of keyable flaps rotatable in opposing rotational directions to maximize the resistance to upwards vertical travel of the anchor during installation to thereby minimize the distance of upward travel of the anchor as it is installed. Additionally, by rotating the flaps in opposing rotational directions as they are transitioned from a run-in position to a set position, any torque applied to the anchor by the flaps is cancelled out, resulting in zero net torque being applied to the anchor by the flaps during installation. In some embodiments, the plurality of flaps may be grouped in pairs each forming a Y-profile when in their set positions. Additionally, each flap pair may rotate in opposed rotational directions (e.g., from the perspective of a longitudinal axis of the anchor) when transitioning to their set positions.

Additionally, embodiments of methods for anchoring an offshore vessel to a seabed positioned beneath a column of water are described herein. In some embodiments, a magnitude of an extraction force applied to a follower of the anchoring system may be monitored by a surface controller to conveniently confirm the successful installation of the anchoring system.

Referring now to FIGS. 1-3, an embodiment of a system 10 for anchoring an offshore vessel to a seabed 3 positioned beneath a water column 5 is shown. Anchoring system 10 may be used to anchor an offshore vessel, such as a floating vessel (e.g., a ship, floating platform, or other floating vessel) to the seabed 3 such that the offshore vessel is prevented from drifting along the water column 5. Anchoring system 10 generally includes an anchor or foundation 20, a plurality of mooring lines 30, a plurality of support members or plates 40, a plurality of keying-flap assemblies 50, and a follower 80 for installing the foundation 20 within the seabed 3. In this exemplary embodiment, foundation 20 has a central or longitudinal axis 25 and comprises a tubular structure extending between a first or upper end 21 and a second or lower end 23 opposite the upper end 21, and includes an exterior surface 22 extending between ends 21 and 23, and an interior surface 24 extending between ends 21 and 23 and defining a cylindrical passage formed within the foundation 20. Particularly, in this exemplary embodiment, foundation 20 comprises a multi-ring anchor (MRA). It may be understood that the geometry of foundation 20 may vary in other embodiments. For example, in some embodiments, foundation 20 may comprise a tubular structure having a cross-sectional geometry that varies from the cross-sectional geometry of foundation 20 shown in FIGS. 1-3 (e.g., the alternative anchor could have a, plate, rectangular, triangular, etc., cross-sectional geometry). In other embodiments, the foundation 20 may not be tubular and instead may comprise one or more non-tubular members having a variety of shapes and configurations and which are embeddable into the seabed 3. Additionally, foundation 20 may be formed from a variety of materials including, for example, steel, concrete, engineering plastic, and composite materials like carbon fiber. Further, foundation 20 may be formed using a variety of fabrication methods including, for example, manufacturing and three-dimensional (3D) printing.

In this exemplary embodiment, the plurality of mooring lines 30 are coupled to the exterior surface 22 of foundation 20 at a plurality of cable connectors 32 spaced circumferentially along the exterior surface 22. In this exemplary embodiment, cable connectors 32 comprise pad-eyes and thus may also be referred to as pad-eyes 32 herein. In this configuration, tension may be transmitted from the mooring lines 30 to the foundation 20 via the plurality of cable connectors 32 coupled therebetween. Mooring lines 30 may comprise metallic chains in some embodiments, but may comprise various materials (e.g., polymer-containing materials) and alternating configurations in other embodiments. The circumferential spacing of cable connectors 32 ensures the tension applied to foundation 20 by mooring lines 30 following the activation or setting of anchoring system 10 is symmetrical about the circumference of the foundation 20.

In this exemplary embodiment, each of the support members 40 of anchoring system 10 extend radially between a radially inner end 42 and a radially outer end 44 opposite inner end 42. Additionally, each of the support members 40 extends longitudinally (generally parallel with central axis 25) between a first or upper end 41 and a second or lower end 43 opposite the upper end 41. Support members 40 are generally plate-like or planar in this exemplary embodiment, but it may be understood that the shape and configuration of support members 40 may vary in other embodiments. For examples, in some embodiments, anchoring system 10 may include only a single support member 40 that extends at an angle (but not necessarily radially) to the foundation 20. In some embodiments, support members 40 may be formed integrally or monolithically with the foundation 20 whereby support members 40 comprise a portion of the foundation 20. In this exemplary embodiment, the inner ends 42 of support members 40 are attached to the exterior surface 22 of the foundation 20 such as by bonding (e.g., welding), through the use of one or more fasteners, or other means. Additionally, in this exemplary embodiment, each support member 40 has a longitudinal length extending between ends 41 and 43 that is approximately equal to the longitudinal length of foundation 20 extending between ends 21 and 23; however, in other embodiments, the longitudinal length of support members 40 may be greater or less than the longitudinal length of the foundation 20.

Keying-flap assemblies 50 of anchoring system 10 are positioned along the upper ends 41 of support members 40 whereby keying-flap assemblies 50 extend generally radially from the central axis 25 of foundation 20. As will be discussed further herein, keying-flap assemblies 50 are configured to resist vertically upwards travel of the foundation 20 during the process for installing the anchoring system 10. In this exemplary embodiment, each keying-flap assembly 50 comprises an elongate collar 52 positioned along the upper end 41 of a given support member 40, a pair of opposed flaps 60, and a pair of hinges 70 pivotably coupling the pair of flaps 60 to the upper end 41 of the support member 40. Hinges 70 define pivot or rotational axes about which flaps 60 are pivotable, where the rotational axes extend generally horizontal and orthogonal to the central axis 25 of foundation 20. In this manner, flaps 60 are grouped into a plurality of flap pairs rotatable in opposing rotational directions from the perspective of a location positioned along central axis 25 of foundation 20.

The collar 52 of each keying-flap assembly 50 defines a pair of opposed inclined stop surfaces 54 extending along the upper end 41 of a given support member 40. The angles formed by the pair of stop surfaces 54 may delimit the maximum rotational travel of flaps 60 relative to the support member 40 as will be discussed further herein. Thus, the inclined angles formed by stop surfaces 54 may be adjusted to suit the given application, where relatively steeper angles delimit a relatively lesser degree of permitted rotational travel of flaps 60 while relatively shallower angles delimit a relatively greater degree of permitted rotational travel of flaps 60.

Each flap 60 of the keying-flap assembly 50 extends between a first or upper end 61 and a second or lower end 63 opposite the upper end 61. The upper end 61 of each flap 60 corresponds to a free end of the flap 60 while the lower end 63 of the flap 60 is hinged to the upper end 41 of a support member 40 via a hinge 70 pivotably coupled therebetween. In this exemplary embodiment, the upper end 61 of each flap 60 comprises a ramped or inclined surface 62 forming a groove between the upper ends 61 of the pair of flaps 60 when the keying-flap assembly 50 is in a first or run-in configuration shown in FIGS. 1-3. Inclined surfaces 62 may assist in transitioning the keying-flap assembly 50 from the run-in configuration to a second or set configuration, as will be discussed further herein. It may be understood that in some embodiments the upper ends 61 of flaps 60 may not include inclined surfaces 62.

The follower 80 assists in running or installing the foundation 20 within the seabed 3 and is removed from the foundation 20 following the installation of the foundation 20 within the seabed 3 as will be further discussed herein. In this exemplary embodiment, follower 80 is generally cylindrical having a first or upper end connected to a setting line or cable 82 that extends to an offshore vessel located at the surface. A second or lower end of the follower 80 longitudinally opposed to the upper end thereof is received in the central passage of the foundation 20 whereby the follower 80 may apply axially directed (e.g., directed along central axis 25 of foundation) to the foundation 20 during the installation thereof. The lower end of follower 80 may be releasably coupled to the foundation 20 whereby the follower 80 may apply axially directed forces to the foundation 20 during the installation thereof and then release from the foundation 20 following the installation thereof such that the follower 80 may be retrieved to the surface leaving the foundation 20 embedded in the seabed 3.

Referring to FIG. 4, an embodiment of an anchor installation or handling vessel 100 is shown located at a waterline 7 of the water column 5 and which is tethered to the anchoring system 10 shown in FIGS. 1-3. Anchor handling vessel 100 is generally configured to facilitate the installation of anchoring system 10 by applying a tension or extraction force to the setting cable 82 coupled to follower 80 of anchoring system 10. In this exemplary embodiment, anchor handling vessel 100 includes a deck 102, and a winch assembly 110. The winch assembly 110 of anchor handling vessel 100 connects the anchor handling vessel 100 with the anchoring system 10 shown in FIGS. 1-3. Particularly, winch assembly 110 comprises one or more winches 112 connected to the setting cable 82 of the anchoring system 10 whereby the setting cable 82 extends vertically upwards through the water column 5 from the follower 80 to the winch 112 of anchor handing vessel 100. While in this exemplary embodiment winch assembly 110 is used to apply tension to setting cable 82, it may be understood that other means may used in other embodiments for applying an extraction force to setting cable 82 such as, for example, a vibratory hammer.

The winch assembly 110 of anchor handling vessel 100 additionally includes a surface controller 120 configured to control the operation of the winch 112 (e.g., control the operation of one or more motors of the winch 112) of winch assembly 110. Particularly, surface controller 120 comprises a computer or computing system and is configured to monitor and potentially control the amount of tension applied to the setting cable 82, and hence the amount of vertically directed load or extraction force applied to the foundation 20 by the winch 112. As will be discussed further herein, in some embodiments, the surface controller 120 is controlled by a human operator. However, in other embodiments, surface controller 120 may control the operation of winch 112 at least semi-autonomously, minimizing the need for personnel onboard the anchor handling vessel 100.

Referring again to FIGS. 1-3, FIGS. 1-3 illustrate the anchoring system 10 in the run-in configuration prior to the installation or setting of the anchoring system 10. FIG. 1 particularly illustrates the anchoring system 10 following penetration of the foundation 20 into and through the seabed 3 where the vertically downwards direction of travel of foundation 20 is indicated by arrow 11 in FIG. 3. Utilizing the weight of foundation 20 and follower 80 along with an added installation force provided by, for example, suction, impact-hammer, or vibratory tool, foundation 20 and follower 80 travel towards an installation depth 12 of the anchoring system 10 that is vertically beneath the seabed 3.

As foundation 20 and follower 80 travel downwards towards the installation depth 12, keying-flap assembly 50 remains in a run-in configuration associated with the run-in configuration of the anchoring system 10. In the run-in configuration of keying-flap assembly 50, as shown particularly in FIGS. 2 and 3, the pair of flaps 60 are oriented in a substantially vertical direction arcuately spaced from the stop surfaces 54 of collar 52. In this arrangement, as best shown in FIG. 2, keying-flap assembly 50 in the run-in configuration has a minimum axially-projected surface area with flaps 60 oriented in the substantially vertical direction generally parallel to the central axis 25 of foundation 20. It may be understood that the resistance to vertical travel through the earthen subsurface region 4 located vertically beneath the seabed 3 is contingent on the amount of axially-projected surface area of the keying-flap assembly 50. Thus, by minimizing the axially-projected surface area of keying-flap assembly 50 when in the run-in configuration thereof, the resistance to vertical travel of the foundation 20 through the subsurface region 4 is concomitantly minimized.

Referring to FIGS. 5-7, anchor system 10 is shown still in the run-in configuration with foundation 20 having reached the installation depth 12 seabed 3 with the entirety of the foundation 20 positioned vertically beneath the seabed 3. In this position, the keying-flap assembly 50 remains in the run-in configuration with flaps 60 oriented in the substantially vertical direction. Additionally, as best shown in FIG. 5, at this stage of the installation of anchoring system 10 tension is initially applied to the setting cable 82 from the surface (e.g., from the anchor handling vessel 100 shown in FIG. 4). The tension applied to setting cable 82 is transferred as a vertically upwards, axially directed force to the foundation 20 from the follower 80 via engagement between the follower 80 and the foundation 20.

Referring to FIGS. 8-10, as tension is increasingly applied to the setting cable 82 attached to follower 80, the follower 80 and foundation 20 coupled thereto begin to travel vertically upwards towards the seabed 3 as indicated by arrow 13 in FIG. 8. As shown particularly in FIGS. 9 and 10, in response to the vertically upwards travel along direction 13 of foundation 20, flaps 60 of keying-flap assembly 50 begins to transition from the run-in configuration to a second or set configuration whereby flaps 60 begin pivoting about their respective rotational axes defined by hinges 70. The presence of inclined surfaces 62 at the upper ends 61 of flaps 60 may assist, by converting at least some of the axially directed force applied by follower 80 to foundation 20 to a horizontally directed force applied to flaps 60, in initiating the pivoting of flaps 60 from their original substantially vertical orientation to an inclined orientation associated with the set configuration of keying-flap assembly 50.

It may be understood that FIGS. 8-10 illustrate keying-flap assembly 50 in a transitional state between the run-in configuration shown in FIGS. 1-3 and 5-7 and the set configuration which will be discussed further herein. It may be noted that as keying-flap assembly 50 transitions from the run-in configuration to the set configuration, the axially-projected surface area of keying-flap assembly 50 gradually increases as flaps 60 of assembly 50 pivot from their vertical orientations to their inclined orientations, resulting in increased interference between the keying-flap assembly 50 and the material or soil defining the subsurface region 4. The resistance to upward travel of foundation 20 along direction 13 gradually increases as the axially-projected surface area of keying-flap assembly 50 increases. As will be discussed further herein, the increase in resistance to upwards travel of foundation 20 may be registered at the surface by the surface controller 120 of anchor handling vessel 100.

Referring to FIGS. 11-13, anchoring system 10 is shown in the set configuration with the follower 80 separated or disconnected from the foundation 20. As described above, resistance to upwards travel of foundation 20 increases as keying-flap assembly 50 transitions from the run-in configuration to the set configuration. The follower 80 is configured to disconnect from the foundation 20 once the keying-flap assembly 50 reaches the set configuration shown in FIGS. 11-13. For example, the follower 80 may be frangibly coupled to the foundation 20 whereby the follower 80 is configured to automatically disconnect from the foundation 20 in response to the application of an axially directed force exceeding a predefined threshold force. Additionally, keying-flap assembly 50 may be configured such that the resistance to upwards travel of foundation 20 achieved when keying-flap assembly 50 is in the set configuration exceeds the predefined threshold force, resulting in the breaking of the frangible connection formed between the follower 80 and the foundation 20 and the disconnection of the follower 80 from the foundation 20.

In this exemplary embodiment, in the set configuration of keying-flap assembly 50, flaps 60 are disposed in their inclined positions resting against or contacting the inclined surfaces 54 of collars 52, thereby preventing further pivoting of flaps 60 about their respective rotational axes. Additionally, in the set configuration of keying-flap assembly 50, the axially-projected surface area of keying-flap assembly 50 is maximized whereby the axially-projected surface area of keying-flap assembly in the set configuration is greater than the axially-projected surface area of the keying-flap assembly in the run-in configuration. In some embodiments, the ratio of the axially-projected surface area of the keying-flap assembly 50 in the set configuration to axially-projected surface area of the keying-flap assembly 50 in the run-in configuration is approximately between 2:1 and 20:1.

Following disconnection of the follower 80 from the foundation 20, the foundation remains embedded within the seabed 3 at an embedment depth 14 that is spaced from the installation depth 12 by a vertical embedment distance 15 such that the embedment depth 14 is positioned between the seabed 3 and the installation depth 12. It may be understood that the increase in resistance to upward travel of foundation 20 provided by the keying-flap assembly 50 as the assembly 50 transitions into the set configuration minimizes the embedment distance 15 separating the installation depth 12 and the embedment depth 14 which thereby more securely anchors the foundation 20 within the seabed 3.

Additionally, given that each support member 40 is coupled to a pair of opposed flaps 60 (the pair of opposed flaps 60 collectively defining a Y-flap when assembly 50 is in the set configuration) of the keying-flap assembly 50, in addition to resisting vertically upwards movement of the foundation 20 through the subsurface region 4, keying-flap assembly 50 also does not produce an undesirable torque on the foundation 20 in response to the application of the upwards directed force against the foundation 20 by the follower 80. Particularly, each pair of flaps 60 generates an opposed rotational torque whereby the torque generated by flaps 60 is essentially cancelled out, resulting in a zero net torque applied to the foundation 20 by the keying-flap assembly 50. For example, a first flap 60 of a given pair of flaps 60 may apply a first torque in a clockwise rotational direction against the foundation 20 while a second flap 60 of the pair of flaps 60 applies a corresponding and substantially equal second torque in the counterclockwise rotational direction against the foundation 20 thereby cancelling out the first torque applied by the first flap 60 of the pair of flaps 60. It may be understood that it is generally desirable to avoid applying torque to the foundation 20 during the setting thereof as such an application of torque could result in the twisting of the foundation 20 during the setting thereof which may compromise the installation of the foundation 20 within the seabed 3.

Referring briefly to FIGS. 14-16, anchoring system 10 is shown in the set configuration following the installation of the foundation 20 within the seabed 3 at the embedment depth 14. As shown particularly in FIG. 14, the follower 80 has been successfully retracted to the surface (e.g., the deck 102 of anchor handling vessel 100. Also, as shown particularly in FIGS. 15 and 16, keying-flap assembly 50 remains in the set configuration following installation of foundation 20 to prevent foundation 20 from being displaced to the seabed 3 in response to tension applied to the foundation 20 from mooring lines 30 attached to the anchor handling vessel 100. In this manner, by varying the resistance to vertical movement of foundation 20 using the keying-flap assembly 50, the foundation 20 may successfully penetrate through the seabed 3 to the installation depth 12 with keying-flap assembly 50 providing a minimal degree resistance to vertical travel, and then may be retained within the seabed 3 at the embedment depth 14 with keying-flap assembly 50 providing a maximal degree of resistance to vertical travel of the foundation 20.

Referring now to FIGS. 17 and 18, another embodiment of an anchoring system 130 is shown including a keying-flap assembly 140. Anchoring system 130 includes features in common with the anchoring system 10 shown in FIGS. 1-16, and shared features are labeled similarly. Particularly, anchoring system 130 generally includes foundation 20, a plurality of circumferentially spaced support members 132, and the keying-flap assembly 140. Additionally, in some embodiments, anchoring system 130 also includes follower 80 for embedding the foundation 20 beneath the seabed 3.

Anchoring system 130 is similar to the anchoring system 10 described above except that support members 132 are circumferentially spaced within the central passage of foundation 20 rather than being positioned external the central passage of foundation 20. In this configuration, support members 132 comprise internal stiffeners of the foundation 20 providing structural support to the foundation 20. The keying-flap assembly 140 of anchoring system 130 includes a plurality of flaps 60 (shown in their set positions in FIG. 18) and remains coupled to the plurality of support members 132 in a configuration similar to the coupling of keying-flap assembly 50 to support members 40 in the anchoring system 10 described above. In this manner, flaps 60 may also be present in the central passage of foundation 20 along with support members 132.

As described above, the transition of the anchoring assembly from the run-in configuration to the set configuration may be automatically registered in at least some embodiments by the surface controller 120 of anchor handling vessel 100. For example, referring to FIG. 19, an exemplary graph 150 is shown illustrating extraction force 152 applied to the foundation 20 by the winch assembly 110 of anchor handling vessel 100 as a function of keying distance which refers to the distance in upwards travel of the foundation 20 from the installation depth 12 beneath the seabed 3. While the extraction force 152 is applied to the foundation 20 by the winch assembly 110 in this example, but it may be understood that the extraction force may be applied by a variety of different mechanisms in other embodiments. Initially, it may be understood that graph 150 is only mean to serve as an example, and in other embodiments the extraction force 152 as a function of keying distance may vary from that shown in graph 150.

The graph 150 of extraction force 152 includes several salient features which may be identified automatically by a computer system such as the surface controller 120 controlling the operation of the winches 112 of winch assembly 110. Initially, in this example, a first transition point of slope decrease 154 in the extraction force 152 occurs between 0.1 meters (m) and 0.2 m of keying distance where the slope of the extraction force 152 declines substantially. In other words, the amount of extraction force 152 required to displace foundation 20 vertically upwards following the first transition point 154 is less than the amount of extraction force 152 required to displace foundation 20 vertically upwards preceding the first transition point 154. The first transition point 154 may correspond to the initiation of the keying-flap assemblies 50 transitioning from the run-in configuration to the set configuration.

In this example, following the first transition point 154, a second transition point of slope increase 156 occurs at approximately 0.3 m of keying distance where the slope of extraction force 152 increases substantially. In other words, the amount of extraction force 152 required to displace foundation 20 vertically upwards following the second transition point 156 is substantially greater than the amount of extraction force 152 required to displace foundation 20 vertically upwards preceding the second transition point 156. The second transition point 156 corresponds to the moment when flaps 60 reach their set positions thereby placing the keying-flap assembly 50 in the set configuration in which the axially-projected surface area of keying-flap assembly is maximized, requiring a significant increase in the extraction forcen 152 in order to pull the anchor 20 farther upwards towards the seabed 3.

Following the second transition point 156, in this example, a third transition point or slope decrease 158 occurs at approximately 0.4 m of keying distance where the slope of extraction force 152 decreases substantially. In other words, the amount of extraction force 152 required to displace foundation 20 vertically upwards following the third transition point 158 is less than the amount of extraction force 152 required to displace foundation 20 vertically upwards preceding the third transition point 158. The third transition point 158 may correspond to the completion of the transition of the keying-flap assembly 50 into the set configuration with each pair of flaps 60 contacting the corresponding stop surfaces 54 of the collars 52 of assembly 50.

In some embodiments, surface controller 120 controls the application of the extraction force 152 so as to successfully install the foundation 20 and keying-flap assembly 50 beneath the seabed 3. For example, the surface controller 120 may automatically identify one or more of the transition points 154, 156, and 158 illustrated in graph 150 to automatically determine the successful transition of the keying-flap assembly 50 into the set configuration. In one example, surface controller 120 may automatically identify the second transition point 156, and hence the successful transition of keying-flap assembly 50 into the set configuration, in response to identifying a doubling of the slope in extraction force 152. In other words, in some embodiments, surface controller 120 automatically identifies the successful transition of keying-flap assembly 50 into the set configuration in response to detecting at least a doubling in the amount of extraction force required to displace the foundation 20 vertically over a given distance. In this manner, surface controller 120 may automatically identify at the surface the successful transition of the keying-flap assembly 50 into the set configuration, reducing the need for personnel onboard anchor handling vessel 100 while increasing confidence in the successful performance of the installation of anchoring system 10.

Referring now to FIG. 20, an exemplary embodiment of an offshore vessel 170 anchored to the seabed 3 by a plurality of anchoring systems 10 is shown. Offshore vessel 170 comprises a floating structure located at the waterline 7 and is connected to a plurality of installed anchor systems 10 each anchored to the seabed 3. Particularly, a plurality of mooring lines 30 of the anchor systems 10 extend between foundations 20 of the anchor systems 10 and a support structure 172 of the offshore vessel 170 thereby tethering the offshore vessel 170 to the plurality of foundations 20. In this exemplary embodiment, offshore vessel 170 comprises a floating offshore wind turbine (FOWT); however, it may be understood that the configuration and function of offshore vessel 170 tethered to anchoring systems 10 may vary significantly depending on the given application. Additionally, in this exemplary embodiment, offshore vessel 170 is supported by a catenary mooring system comprising the plurality of anchoring systems 10. However, it may be understood that offshore vessel 170 may be supported by a variety of different mooring systems comprising anchoring systems 10 such as semi-taut mooring systems, taut mooring systems, tension leg mooring systems, and length-varying tension-fixed (LVTF) mooring systems.

As an example, and referring to FIG. 21, an embodiment of a computer system 200 is shown suitable for implementing one or more embodiments disclosed herein. For example, the surface controller 120 of FIG. 4 may comprise the computer system 200 or at least some of the features of computer system 200. The computer system 200 of FIG. 22 includes a processor 202 (which may be referred to as a central processor unit or CPU) that is in communication with memory devices including secondary storage 204, read only memory (ROM) 206, random access memory (RAM) 208, input/output (I/O) devices 210, and network connectivity devices 212. The processor 202 may be implemented as one or more CPU chips. It is understood that by programming and/or loading executable instructions onto the computer system 200, at least one of the CPU 202, the RAM 208, and the ROM 206 are changed, transforming the computer system 200 in part into a particular machine or apparatus having the novel functionality taught by the present disclosure.

Additionally, after the system 200 is turned on or booted, the CPU 202 may execute a computer program or application. For example, the CPU 202 may execute software or firmware stored in the ROM 206 or stored in the RAM 208. In some cases, on boot and/or when the application is initiated, the CPU 202 may copy the application or portions of the application from the secondary storage 204 to the RAM 208 or to memory space within the CPU 202 itself, and the CPU 202 may then execute instructions that the application is comprised of. In some cases, the CPU 202 may copy the application or portions of the application from memory accessed via the network connectivity devices 212 or via the I/O devices 210 to the RAM 208 or to memory space within the CPU 202, and the CPU 202 may then execute instructions that the application is comprised of. During execution, an application may load instructions into the CPU 202, for example load some of the instructions of the application into a cache of the CPU 202. In some contexts, an application that is executed may be said to configure the CPU 202 to do something, e.g., to configure the CPU 202 to perform the function or functions promoted by the subject application. When the CPU 202 is configured in this way by the application, the CPU 202 becomes a specific purpose computer or a specific purpose machine.

Secondary storage 204 may be used to store programs which are loaded into RAM 208 when such programs are selected for execution. The ROM 206 is used to store instructions and perhaps data which are read during program execution. ROM 206 is a non-volatile memory device which typically has a small memory capacity relative to the larger memory capacity of secondary storage 204. The secondary storage 204, the RAM 208, and/or the ROM 206 may be referred to in some contexts as computer readable storage media and/or non-transitory computer readable media. I/O devices 210 may include printers, video monitors, liquid crystal displays (LCDs), touch screen displays, keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, or other well-known input devices.

The network connectivity devices 212 may take the form of modems, modem banks, Ethernet cards, universal serial bus (USB) interface cards, wireless local area network (WLAN) cards, radio transceiver cards, and/or other well-known network devices. The network connectivity devices 212 may provide wired communication links and/or wireless communication links. These network connectivity devices 212 may enable the processor 202 to communicate with the Internet or one or more intranets. With such a network connection, it is contemplated that the processor 202 might receive information from the network, or might output information to the network. Such information, which may include data or instructions to be executed using processor 202 for example, may be received from and outputted to the network, for example, in the form of a computer data baseband signal or signal embodied in a carrier wave.

The processor 202 executes instructions, codes, computer programs, scripts which it accesses from hard disk, floppy disk, optical disk, flash drive, ROM 206, RAM 208, or the network connectivity devices 212. While only one processor 202 is shown, multiple processors may be present. Thus, while instructions may be discussed as executed by a processor, the instructions may be executed simultaneously, serially, or otherwise executed by one or multiple processors. Instructions, codes, computer programs, scripts, and/or data that may be accessed from the secondary storage 204, for example, hard drives, floppy disks, optical disks, and/or other device, the ROM 206, and/or the RAM 208 may be referred to in some contexts as non-transitory instructions and/or non-transitory information.

In an embodiment, the computer system 200 may comprise two or more computers in communication with each other that collaborate to perform a task. For example, but not by way of limitation, an application may be partitioned in such a way as to permit concurrent and/or parallel processing of the instructions of the application. Alternatively, the data processed by the application may be partitioned in such a way as to permit concurrent and/or parallel processing of different portions of a data set by the two or more computers. In an embodiment, the functionality disclosed above may be provided by executing the application and/or applications in a cloud computing environment. Cloud computing may comprise providing computing services via a network connection using dynamically scalable computing resources.

Referring to FIG. 22, an embodiment of a method 220 is shown for anchoring an offshore vessel (e.g., offshore vessel 170 shown in FIG. 20) to a seabed (e.g., seabed 3 shown in FIG. 1) positioned beneath a column of water. Beginning at block 222, method 220 comprises penetrating an anchoring system (e.g., anchoring system 10 shown in FIG. 1 and anchoring system 130 shown in FIG. 17) comprising a foundation (e.g., foundation 20 shown in FIG. 1) and a follower (e.g., follower 80 of FIG. 1) through the seabed to an installation depth (e.g., installation depth 12 shown in FIG. 1) located beneath the seabed. At block 224, method 220 comprises applying an extraction force to the follower whereby the extraction force is transmitted to the foundation.

At block 226, method 220 comprises transitioning a keying-flap assembly (e.g., keying-flap assembly 50 shown in FIG. 3 and keying-flap assembly 140 shown in FIG. 18) comprising a plurality of flaps (e.g., flaps 60 shown in FIGS. 3 and 18) pivotably coupled to the foundation from a run-in configuration in which each of the flaps occupies a first position to a set configuration in which each of the flaps occupies a second position pivoted from their first position in response to transmitting the extraction force to the foundation. In some embodiments, block 226 comprises applying an extraction force to the follower of the anchoring system via a setting line (e.g., setting line 82 shown in FIG. 1) connected between the follower and a winch located on a surface anchor handling vessel (e.g., anchor handling vessel 100 shown in FIG. 4). At block 228, method 220 comprises monitoring by a surface controller (e.g., the surface controller 120 shown in FIG. 4) spaced from the foundation a magnitude of the extraction force (e.g., extraction force 152 shown in FIG. 19) as the keying-flap assembly is transitioned from the run-in configuration to the set configuration to automatically confirm that the keying-flap assembly has successfully transitioned to the set configuration.

Experiments were conducted pertaining to systems and methods for connecting a plurality of separate vehicles together using hard connects to form a vehicle platooning system. Initially, it may be understood that the following experiments described herein are not intended to limit the scope of this disclosure and the embodiments described above and shown in FIGS. 1-22.

MRAs have been developed as a cost-effective and networked anchor solution to secure floating structures placed in arrays into the seabed. The MRA’s combined features of fewer, smaller, and lighter anchors permit significant capital cost savings such as material, fabrication, transport, and installation, resulting in the competitiveness of FOWTs economically. However, the relatively shorter length of the MRA than the conventional caisson requires features such as keying flaps and wing plates to achieve parity in load capacity with the caisson having the same diameter. Preliminary studies indicated that wing plates attached to the MRA in soft clay have a clear impact on improving its horizontal load capacity, but a relatively lesser effect on enhancing vertical load capacity. This spurred the current experimental study to investigate the role of MRA features, with a specific focus on keying flaps and their applications in the stiffeners and wing plates for enhancing uplift resistance further. Upper bound plastic limit analysis (PLA) was developed to evaluate how keying flaps impact the failure mechanism of the stiffeners and provide reliable estimations of the vertical load capacity of the stiffeners. The validity of the suggested upper bound PLA solutions was demonstrated through comparisons to rigorous two-dimensional finite element (2-D FE) results. The results indicated that PLA can be a more straightforward and computational-effective means to investigate the keying flap’s uplift resistance with a satisfactory agreement with FE-computed values. For the optimal design of the stiffeners, a parametric study based on 2-D FE analyses was also conducted to evaluate the effects of keying flap parameters on the uplift resistance. Additionally, a series of comparative studies of the MRA to the caisson in soft clay indicates the features of the MRA to be more efficient under vertical loading. The studies indicated that incorporating keying flaps can be a cost-effective alternative for enhancing uplift resistance in addition to being less sensitive to soil disturbance during the anchor installation.

Although installable in any soil type, the experimental study described herein focused on performance in soft clay. Additionally, for versatile use in all types of mooring systems such as catenary, semi-taut, taut, tension-leg mooring or length-varying tension-fixed (LVTF) mooring systems, there was a need to develop further for the MRA to achieve parity with a suction caisson of comparable diameter under vertical loading. Introducing keying flaps could be one solution to improve this parity in performance. Thus, this experimental study conducted two-dimensional finite element analyses to understand how keying flaps affect the failure mechanism of a stiffener and to provide reliable evaluations of the increase in uplift resistance attributable to keying flaps.

The mechanisms of the uplift resistance of the MRA can be best illustrated through the comparison to a conventional suction caisson (SC). Although two anchors are similar, differences in the uplift resistance between two anchors can be significant. Particularly, it has been shown that the reverse end bearing is a component of the uplift resistance of the SC, which does not develop for the MRA. Due to a relatively shorter length and deeply embedded condition, the MRA also cannot have additional side resistance extending to the surface, which is indicated in the case of the SC. Side resistance along the interior cylindrical surface of the MRA can partially offset these effects; however, the axial capacity of the MRA must still be enhanced through other means to achieve parity with a SC of similar diameter. Preliminary findings from rigorous analytical calculations on the effects of wing plates and stiffeners currently in progress show that the axial capacity can be improved by increasing diameter, installing wing plates, or introducing keying flaps.

According to previous studies, increases in thickness of the plate anchor are expected to increase bearing factor and axial capacity. Likewise, the uplift resistance of the stiffener can likely be improved by increasing the thickness of the stiffeners t_stf. On the other hand, thicker stiffeners mean that the capital costs like material and fabrication costs, which are dependent on the total dry weight of the anchor, will increase with increasing t_stf. Thus, this study conducted two-dimensional fine element (2-D FE) analyses to understand the effect of the keying flaps on uplift resistance and demonstrate it by comparison to the effect of t_stf on uplift resistance.

In this experimental study, the soil around the MRA plate assumed as the linearly elastic-perfectly plastic behavior below a Tresca yield surface and associated flow rule at the yield. For approximating the undrained loading condition, a Poisson’s ratio assumed µ = 0.49. A uniform undrained shear strength profile was considered s_u = 1 kPa due to the simplicity and convenience of calculations; the only interest was the relative changes in uplift resistance. Noting that the ultimate load capacity was independent of elastic response, Young’s modulus was taken as a ratio Els_u=800. FE simulations for all cases in this experimental study assumed full bonding between the soil and the anchor surface. Because of the deep embedment depth of the anchor and no gapping conditions, the soil could be assumed as weightless in the FE study.

. Referring to FIG. 23, a diagram 250 of postulated failure modes for a Y-shaped keying flap is shown. The FE analyses considered a 1-m length of the MRA plate L_M-pl with keying flaps lengths L_fl varying 0.1 m to 0.3 m, as defined in diagram 250. The flap angle θ_fl varied from 0° to 90°. To estimate the effects of the keying flaps on uplift resistance, L_M-pl, L_fl, and θ_fl were considered as parameters for the parametric study. For the sensitivity of L_fl or θ_fl to the collapse load, a typical thickness of the flap t_fl and MRA plate t_M-pl assumed as the same thickness t_fl=t_M-pl=0.05 m. In the study for estimating the effects of thickness or length of the MRA plate without flaps, L_M-pl/t_M-pl ratio varied from 100 to 7. First-order, fully integrated elements (CPE4) were adopted as the soil model, and the boundary was placed five MRA plate lengths 5L_M-pl away from the MRA plate. The far-field was modeled using one-way infinite elements. Referring to FIG. 24, a graph 260 is shown illustrating normalized axial capacity (V/V_max) as a function of adhesion factor (α) is shown for different (αθ_fl) relationships. The extremely fine mesh was adopted for the accuracy of the analyses. Element dimensions varied from 1/250 of L_M-pl near the MRA plate circumference to 1/20 of L_M-pl in regions far from the MRA plate as indicated in graph 260.

. Given that the case of the MRA plate without keying flaps corresponds to that of thin plate, the FE model in this study can be validated using upper bound estimates for the thin plate. FE computed bearing factors based on loading directions and aspect ratio were given to compare with that of the plate anchor. In the translation of a thin plate normal to its long axis, termed horizontal loading, the FE computed lateral bearing factor is N_p=11.64, which agreed well with the upper bound solution for a thin plate having the same aspect ratio of length to thickness L_pl/t_pl=20. However, the same level of the agreement did not appear for the validation of vertical loading cases. Previous studies present that the upper bound approach consistently overestimates compared to FE estimates. Likewise, the FE computed axial bearing factor N_a=3.1 indicated a reasonable agreement even if it is 12.73% greater than the simplified adjusted form. A similar level of agreement could be obtained by comparing FE estimates for various aspect ratios. Additionally, the agreement between the previous FE studies and FE calculations in this experimental study encouraged the reliability of the FE model for evaluating keying flap effects.

Additionally, various FE studies were performed to understand how the MRA plate with or without keying flaps alters the collapse mechanism and uplift resistance. Referring to FIG. 25, another diagram 270 of a keying-flap assembly is shown in both the run-in and set configurations. With reference to diagram 270, the present experimental study assessed the influence of the following parameters on vertical load capacity: (1) the relative length of the keying flaps, a = L_fl/L_M-pl (2) the angle between the applied load and the plane of keying flaps, θ_fl, and (3) the adhesion factor between soil and the MRA plate, α. As the basis for the parametric study, the MRA plate had a 1-m length with or without keying flaps. Keying flap length varied from 0.1 m (a = 0.1) to 0.3 m (a = 0.3). To figure out the effect of the flap angle θ_fl, the FE study considered the θ_fl varying from 0° to 90° for each case. In the case of a typical MRA plate without keying flaps, aspect ratios L_M-pl/t_M-pl varying from 100 to 7 were taken to understand how the thickness and length impact the uplift resistance of the MRA plate. These have the same length L_M-pl = 1 m for the sensitivity of t_M-pl and the same thickness t_M-pl = 0.05 m for the sensitivity of L_M-pl to uplift resistance of the MRA plate

Previous studies indicated that the axial bearing factor N_a of the stiffener having a single flap can increase depending on the relative flap length a (= L_fl/L_stf). Not intending to be bound by any particular theory, the non-dimensional axial bearing factor Na may be expressed in accordance with Equation (1) below, where a represents the ratio of the L_fl/L_M-_pl, F represents the collapse load of the MRA plates with or without keying flaps, s_u represents the undrained shear strength of soil, and L_M-pl represents the length of the stiffener or wing plate:

$\begin{matrix} N_{a} (a, θ_{f l}) = \frac{F}{s_{u} L_{M - p l}} & (1) \end{matrix}$

In comparing the cases of a = 0.1 and a = 0.2, N_a increased with increasing L_fl. By contrast, even though the case of a = 0.3 had longer flap length, the N_a was similar to that of the case of a = 0.2. In actuality, the stiffener having Y-shaped flaps was needed to consider to estimate the flap length effects. In the case of Y-shaped keying flaps, likewise single keying flap, the flap length L_fl was one of the critical parameters to enhance the uplift resistance. Referring to FIG. 26, a graph 280 illustrating N_a as a function of flap angle (θ_ƒl) is shown for different a values. Particularly, graph 280indicated that N_a increases as L_fl increases. This is a direct consequence of the symmetrical geometry of the Y-shaped flaps, which induce rigid wedge translation upward. As L_fl is increased, the projected length L_p normal to loading direction increases, resulting in a greater rigid wedge that impacts on increasing the uplift resistance. Referring to FIG. 27, another graph 290 is shown illustrating normalized axial capacity as a function of the adhesion factor for different (α) relationships. Additionally, the increasing trend of the axial bearing factor N_a also agrees with the sensitivity of L_fl to V_M-pl, as shown in graph 290 of FIG. 27. This implied that the longer L_fl has a greater impact on increasing V_stf when the MRA plate has the same length L_M-pl.

. In the case of the single keying flap, N_a increased by up to 50% as the flap angle θ_fl increased. Additionally, a more pronounced increasing trend of N_a occurred for longer L_fl. This implied that increasing θ_fl leads to progressively greater bearing resistance of the stiffener. A more pronounced trend occurred in the case of Y-shaped flaps as indicated in graph 280. Particularly, N_a of Y-shaped flaps increased by up to 160% with increasing θ_fl. This increasing trend of N_a has shown more clearly in the case of longer L_fl. When the keying flaps were imposed, the collapse mechanism of the MRA plate was changed depending on flap angle and length, resulting in enhancing bearing resistance. Improved bearing resistance permits the MRA plate to be less sensitive to soil adhesion or disturbance that occurred from anchor installation.

.Particularly, a typical MRA plate without keying flaps is dependent on frictional resistance along the side, especially the adhesion between soil and the MRA plate. By contrast, the keying flaps can alter the failure mechanism of the MRA plate and enhance the uplift resistance. To determine the effect of the adhesion factor on the Y-shaped flaps, adhesion factors α = 0.1, 0.4, and 0.7 were considered. When the keying flaps were imposed under general adhesion conditions, keying flaps also alter the collapse mechanism of the MRA plate, which led to enhancing the bearing resistance. Additionally, unlike the full adhesion condition, frictional resistance occurred along the side in the case of general adhesion as indicated in graphs 260 and 290 of FIGS. 24 and 27. As the adhesion factor decreases, also indicated in graphs 260 and 290, uplift resistance V_M-pl decreased. A more pronounced decreasing trend of V_M-pl occurs for lower flap angle θ_fl or shorter flap length L_fl. This suggested that the MRA plate with keying flaps can be a more reliable solution having less sensitivity to frictional resistance in addition to soil disturbance during anchor installation

In the case of a typical MRA plate, likewise a simple thin plate anchor, the vertical load capacity consists of the side frictional resistance and end bearings at the top and tip. Previous studies indicated that a simple plate is dependent on side resistance generated by the adhesion factor between soil and plate. These implied the uplift resistance of the MRA plate increased with increasing MRA plate length L_M-pl or MRA plate thickness t_M-pl. FE results produced by this experimental study confirmed that a longer or thicker MRA plate can improve the uplift resistance

Material and fabrication costs account for approximately 45 percent of the total capital cost for the MRA in a clay seabed, and an optimal anchor design should be required to reduce capital costs. As the material and fabrication costs are directly dependent on anchor size and these costs are in proportion to unit steel price of bulk and unit fabrication price of bulk, indicative cost analyses based on total dry unit weight W_dry can provide useful comparisons to optimize the anchor size. Thus, this experimental study carried out indicative cost analysis to optimize the MRA plate size, among a longer MRA plate, a thicker MRA plate, or a MRA plate having keying flaps. The results of this experimental study indicated that introducing keying flaps can be a more cost-effective means with comparable uplift resistance compared to longer or thicker MRA plates. Particularly, introducing keying flaps can double or have comparable load capacity compared to the longer or thicker MRA plates as well as keeping one-third or one-fourth of that of material and fabrication cost. Thus, keying flaps should be considered as a cost-effective solution to enhance the axial load capacity

Additionally, the FE predictions produced by this experimental study indicated that the axial bearing factor N_a of the MRA plate having keying flaps increased up to N_a=8 under L_fl/L_stt=0.3 and θ_fl=90°. This also implied that N_a increases as keying flaps are engaged in soil. In order to present effectively how keying flaps impact on the vertical load capacity of the MRA in soft clay, the simplified bearing factor N_s can be replaced as the axial bearing factor N_a considering the effects of keying flaps. Results of this experimental study indicated that the relative uplift capacity of the MRA can be improved when keying flaps on the stiffeners or wing plates are engaged in soil. This suggested that the MRA can get more additional uplift resistance by introducing keying flaps, in which the increase can vary depending on flap length L_fl and flap angle θ_fl. For example, the MRA having Y-flaps on the wing plates can more than double the resistance of an MRA of the same size, but without Y-flaps. Additionally, the MRA plate having keying flaps can enhance the axial load capacity with less sensitivity to adhesion factor between soil and pile as well as the soil disturbance during installation, as indicated by graphs 260 and 290.

In summary, this experimental study conducted two-dimensional FE analyses to understand how keying flaps can alter the failure mechanism and to evaluate the effects of the keying flap on the MRA performance under vertical loading. Upper bound PLA models were suggested and validated by comparison to the FE result, where a satisfactory agreement between PLA and FE can provide improved confidence in the solutions. Additionally, a series of sensitivity studies were carried out to figure out the potential advantages of keying flaps for the optimal design of the stiffener, associated with the uplift resistance of the MRA in soft clay. Basic conclusions of this experimental study were as follows: (1) Uplift resistance V increased as the length of the MRA plate L_M-pl increased. But it was primarily dependent on side resistance, which is affected by adhesion. (2) Uplift resistance V increased with increasing the thickness of the MRA plate t_M-pl. (3) In actuality, Y-shaped flaps needed to be considered to estimate the keying flap effects for the optimal design of the MRA plate. (4) Uplift resistance V increased as the flap angle θ_fl increased. The trend of increasing load capacity V also occurred with increasing flap length L_fl. and(5) Introducing keying flaps on the stiffeners or wing plates can be a more cost-effective means to enhance the vertical load capacity of the MRA in soft clay, as well as have less sensitivity to adhesion factors and soil disturbance that occurred during anchor installation.

While embodiments of the disclosure have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.

OFFSHORE ANCHORING SYSTEMS AND ASSOCIATED METHODS

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